1. Field of the Invention
This invention relates generally to four-sided clipless bicycle pedals and more particularly to a method of manufacturing such pedals.
2. Background Art
Originally, pedals were simply platforms to push down on. Then came pedals with toe clips, which were essentially cages on top of the pedals that the rider's shoes fit into. Then came “clipless” pedals, which securely held rider's shoes to the pedals without the toe clip (hence “clipless”).
A number of clipless pedal designs have been made commercially available. A clipless pedal is a pedal that clamps to the rider's shoe via a cleat mounted to the bottom of the rider's shoe. Typically, to unclip the rider twists his foot outwards. The first clipless pedals were single side entry because they had latch and release mechanisms on only one side of the pedal. The next clipless pedals were double side entry because they had latch and release mechanisms on opposite sides of the pedal. The advantage of double side entry is that it is easier for the rider to clip into the pedal without looking. The disadvantage is that double side entry pedals are generally more complex and heavier than single side entry pedals. The next clipless pedal was four-sided, and had the advantage of making it even easier for the rider to clip into the pedal, improved performance in mud, lighter weight, and greater simplicity. The disadvantage of the four-sided pedal is a relatively high manufacturing cost.
A four-sided pedal is disclosed in U.S. Pat. No. 6,205,885 to the present inventors. Even with its relatively high manufacturing cost, this pedal has achieved significant success in the marketplace. However, the success will always be limited by the cost. For example, there are perhaps ten times more pedals sold at US$60 retail than at US$120 retail. The technology of the four-sided pedals is extremely good and well proven in the market, but the cost of manufacture is simply too high for selling to the largest segment of the market. That is why it is important to be able to manufacture the clipping mechanism in a more efficient manner.
The '885 patent describes a four-sided pedal that is made using bent wire/machining/welding processes for the clipping mechanism. It describes other methods of manufacture such as forging or machining. The problem with using bent wire/machining/welding processes for the clipping mechanism is that the machined parts are somewhat complex and it is difficult to accurately align all the parts during the welding process.
Forging the clipping mechanism would be very expensive because there are still a great number of steps in the process and the flash is difficult to trim. It is especially difficult to trim the flash because the parts must remain straight or else they will not function properly and it takes a large force for trimming.
Machining the clipping mechanism as described in the '885 patent is also expensive because of the protrusions and because there is multi-axis machining required. Also, the spring shown in the preferred embodiment of the '885 patent is difficult to make, because the wire is bent back over itself.
The clipping mechanism of the actual four-sided clipless pedals currently marketed under the '885 patent is made using investment casting (also called lost wax casting). Investment casting works extremely well functionally for making these parts, but is so labor intensive that it is expensive. Also, it is difficult to investment cast these parts straight because the clipping bars are relatively thin and especially fragile when still in their wax state. The '885 pedal currently marketed has two investment cast components. Therefore, a pair of pedals requires four investment cast components. These four components can easily cost more than the rest of the pedal components combined.
Another problem with investment casting the clipping mechanism of the pedal is that because there are so many steps to the process, the lead time for making parts is long. Typical lead time is almost two months for production quantities. This can cause delivery problems if demand exceeds expectations. Also, capacity can be a problem because most casting companies have a relatively low daily output. Investment casting is normally a process used for low volume production.
As discussed above, investment casting is expensive because it involves so many labor intensive steps. Specifically, first a wax positive is injection molded including a sprue and small protrusions (that will become vents). Then several wax positives are joined to a wax “tree” by the sprue. Then this tree is repeatedly dipped into a wet plaster-like slurry that adds layer after layer of plaster. Then the wax is melted away in a high temperature kiln. At this stage, the plaster is a one-time use mold. Then the mold is placed into the investment cast machine and molten metal is poured into the mold. (For titanium, a special investment cast machine is used that keeps the molten titanium in a vacuum.) Then the plaster mold is dissolved to free the metal “tree”. If the metal used is hardenable such as the 17-4ph stainless steel used for most of the marketed pedals currently made under the '885 patent, then each part should be annealed, or else they are too hard to easily cut or machine. Then each part is cut off from the “tree”. Then each part has the sprue cut away more completely. Then each part is machined and finished. It is no surprise that investment casting is so expensive.
Die casting is an inexpensive process that in theory could be used for making the clipping mechanism. Unfortunately, die casting can normally only be used to cast weaker metals such as zinc, aluminum and magnesium. These metals can't be reasonably used for the bars primarily because there is a size limitation. If the bars are made big enough so that zinc or aluminum or magnesium are strong enough, then the profile of the cleat becomes bigger, which causes the cleat to protrude too far from the bottom of the shoe to allow easy walking. Also, it would increase the distance from the bottom of the rider's foot to the center of the axle (called stack height). It is advantageous to have the lowest stack height possible. Also, die cast metals such as zinc, aluminum and magnesium are so soft that they would wear more quickly, especially where the cleat rubs against the clipping mechanism. Therefore, steel or titanium or other high strength materials should be used for the clipping mechanism.
There is a process known as Metal Injection Molding (MIM) that could conceivably be used to make the clipping mechanism. MIM is, essentially, a sophisticated die casting process that can be used to make steel and other hard metal components. A mixture of powdered metal and a binder material is injection molded into an over-sized part. Then most of the binders are removed during a thermal debinding process. Then the remaining binders are removed in a high-temperature sintering furnace. During the sintering process, the parts shrink about 20%, and metal powder particles fuse together. Unfortunately, MIM, while less labor intensive than investment casting, requires expensive tooling, expensive material preparation, expensive equipment, and several steps. The piece cost is similar to investment casting. Therefore, it would still be a relatively expensive process to use for making the clipless mechanism.
In order to achieve the goal of participating in the lower priced category, the price of the clipping mechanism components should be reduced not by a few percent, but by a factor of 5 or 10.